1. Field of the Invention
The invention relates to a piezoelectric adjusting element in accordance with the preamble of patent claim 1.
2. Description of the Related Art
Linear piezoelectric motors whose functionality is based on the utilization of travelling waves are part of the state of the art and are, for example, the subject-matter of the printed patent specifications EP 0 475 752 B2 and U.S. Pat. No. 5,596,241.
Motors of this type suffer from the disadvantage that it is impossible to minimize them to any desired dimensions, because the minimum length of their wave guides must be a multiple value of 6xcex to 10xcex of the wave that expands in them. Moreover, from a technological perspective, they are difficult to manufacture, very complicated in terms of their setup and, therefore, correspondingly expensive.
Also known are piezoelectric motors whose functionality relies on standing acoustic waves. Prior art of this kind is reflected, among others, in U.S. Pat. No. 5,453,653. The motor of this style of execution can be realized small enough and allows, in terms of technology, for the production of major piece numbers. A monolithic piezoelectric oscillator is used as the drive element for this motor; and the oscillator has a long side, a short side as well as a friction element that is arranged on the small surface of the short side. On the first large side, the piezoelectric oscillator is equipped with a first group of electrodes and with a second group of electrodes. A joint electrode is arranged on the second large side. Two areas of a metallized piezo-ceramic surface, which are of equal size and arranged in a rectangular and diagonal manner, cover each first and second group of electrodes. An oscillator supplies electric a.c. voltage to the joint electrode and to the first or to the second group of electrodes. Due to the asymmetrical style of execution of each of the two groups of electrodes in relation to the longitudinal axis of the piezo-plate, an asymmetrical deformation results. This causes the friction element to perform a movement along closed paths either in the one direction or in the other direction, depending on which group of electrodes is supplied with the electric voltage.
The moving friction element sets a pressed-on driven element in motion which, in turn, performs movements in the one direction or in the other direction. The motor is excited with a frequency that is close to the frequency of resonance of the second vibration mode of the bending vibrations of the piezo-plate in its longitudinal direction.
In piezoelectric motors of this construction type, longitudinal vibrations of the oscillator pass the energy, that is stored inside the oscillator, on to the driven element. The parameters of these vibrations determine the size of the supply voltage of the motor, the geometry of the motor and the overall construction of the motor.
The supply voltage of the piezoelectric motor addressed here must be chosen very high by way of the small electro-mechanical coupling coefficient of the bending modes of the oscillator vibrations. Furthermore, in a piezoelectric motor of this construction type, the driven element has a strong dampening effect on the bending oscillator, which further increases the necessary supply voltage. Accordingly, piezoelectric oscillators in motors of known styles of execution in accordance with the state of the art require supply voltages of up to 500 V, resulting is a corresponding need for high voltage protection.
The relationship between the dimensions of the long side of the oscillator plate and the short side is approximately 3.7 in piezoelectric motors that are versions of the state of the art. With its short side, the oscillator plate is arranged parallel in relation to the surface of a driven element, and it bends along its long side during the operation of the motor. This kind of motor construction limits the maximum possible force that is generated by the motor by way of the flexural strength of the oscillator plate.
Since the friction element is located on the short side of the oscillator plate, its dimensions are limited. The width of the friction element may not be larger than one third of the short side of the piezo-element. This way, consequently, the width of the friction contact is limited to approximately 0.3 . . . 0.4 mm in construction types of motors according to the state of the art. The fact that this width of the friction contact is minimal additionally considerably limits the force that is to be generated by the motor. Correspondingly, motors of the construction types that are known in the art, which are comprised of an oscillator, only achieve a maximum force of approximately 10 N. Moreover, the small width of the friction contact also increases wear and tear, thereby resulting in the temporary instability of the operation of the motor. The small width of the friction contact especially reduces the movement stability of the driven element at low rates of motion. Furthermore, the narrow friction contact leads to parameter changes of the motor when the motor is stored over longer periods of time.
A motor construction in accordance with U.S. Pat. No. 5,453,653 envisions only one friction element on the surface of a piezoelectric oscillator. This causes the piezoelectric oscillator to become mechanically unstable, thereby reducing its positioning accuracy and rendering the construction of the oscillator mounting more complicated.
In addition to the above, one friction element limits the maximum possible force that is generated by the motor with a piezoelectric oscillator. If several oscillators are used, which are combined into a package, the positioning accuracy of the driven element deteriorates, and the electronic motor control is, moreover, very complicated in terms of its realization.
Therefore, it is the subject-matter of the present invention to design a piezoelectric motor on the basis of a monolithic piezoelectric oscillator and that will allow achieving greater force with a smaller excitation voltage, a better operating stability with a longer serviceable life, a more even movement of the driven element at lower rates of motion, a higher parameter stability when the motor is stored for longer periods of time, a mechanically robust oscillator construction, and that allows for a controlling means for tracking the oscillator frequency of resonance and for regulating position and parameters of the driven element.
This object is achieved with a piezoelectric adjusting element, in particular a piezoelectric motor as claimed in patent claim 1.
The piezoelectric motor according to the invention is comprised of a housing, a driven element, a friction layer, which is located on the housing or on the driven element, and of a drive element, which is electrically connected to an electric exciter source containing at least one friction element that is in friction contact with the friction layer, in the form of at least one monolithic plate-shaped or cylindrical piezoelectric oscillator with first and second main surfaces, first and second side surfaces as well as first electrodes and second groups of electrodes that are arranged on its main surfaces.
In the present context, it is essential that the piezoelectric oscillator referred to above has a resonant length and a resonant height, and the first group of electrodes and the second group of electrodes constitute two generators of acoustic waves. Accordingly, the first generator excites a standing longitudinal acoustic wave that vibrates in the direction of the oscillator resonant length. Analogously, the second generator excites a standing longitudinal acoustic wave that vibrates in the direction of the oscillator resonant height. The oscillator resonant length is equal to an integral multiple of the wave length of the standing acoustic longitudinal wave vibrating in its direction, which is generated by the first generator; and the oscillator resonant height is equal to one half of the wave length of the standing acoustic longitudinal wave vibrating in its direction, which, on its part, is generated by the second generator. The size of the oscillator resonant length and/or of the oscillator resonant height is, in particular, subject to the condition that the frequencies of the standing acoustic longitudinal waves, that vibrate in the oscillator in the direction of the oscillator resonant length and the oscillator resonant height, are equal.
The realization of the oscillator resonant length and of oscillator resonant height described here allows for the attachment of friction elements to the side surfaces of the oscillator and for the arrangement of the oscillator plate with its long side along the surface of driven element. In realizations of oscillator constructions of this type, the longitudinal vibrations along the length of the oscillator plate represent the main vibrations that pass the energy stored inside the oscillator on to the driven element. This vibration mode has a higher electro-mechanical coupling coefficient than the mode of the bending vibrations, thereby allowing for a reduction of the excitation voltage of the oscillator.
Due to the fact that the second vibration type of the vibrations that are utilized for the proposed motor consists of the longitudinal vibration mode in the direction of the height of the oscillator plate, it is possible to approximately double the oscillator height. This increases the longitudinal rigidity of the oscillator plate, and the maximum force that can be generated by this oscillator increases. Also, it is possible to attach friction elements with larger widths of friction contact to an oscillator of this kind. This realization also affects an increase of the possible force that is generated by the oscillator. The oscillator construction according to the invention allows for attaching several friction elements, either on one of the side surfaces of the oscillator or on two side surfaces simultaneously. This makes the oscillator considerably more robust, thereby greatly improving the stability of the motor operation at low rates of motion of the driven element.
The large width of the friction contact reduces the wear and tear of the friction element and lowers the extent of the parameter changes of the motor during storage.
A first embodied example of the proposed piezoelectric motor provides that the standing acoustic longitudinal wave, which vibrates along the resonant height of the piezoelectric oscillator, has a constant preceding sign along the resonant length. This motor variant allows for arranging one or two friction elements on one of the side surfaces of the oscillator.
In another embodied example of the proposed piezoelectric motor, the standing acoustic longitudinal wave, which expands along the resonant height of the piezoelectric oscillator, has a variable preceding sign along the resonant length. This motor variant allows for arranging one, two or three friction elements on one of the side surfaces.
In the proposed piezoelectric motor, the electrodes of the first group, i.e. the electrodes constituting the first generator of acoustic waves, are arranged primarily in the margin areas of the main surfaces of the oscillator; in particular, they are arranged symmetrically with regard to the plane of symmetry that extends through the center of the resonant height of the oscillator. And the electrodes of the second group, i.e. the electrodes constituting the second generator of acoustic waves, are arranged in the center area of the main surfaces of the oscillator; in particular, they are arranged symmetrically with regard to the plane of symmetry referred to previously.
An electrode configuration of this kind allows for the independent excitation of a standing acoustic longitudinal wave in the oscillator that vibrates in the direction of the resonant length and of another standing acoustic longitudinal wave that vibrates in the direction of the resonant height.
Another advantageous embodied example of the piezoelectric motor provides that the first group of electrodes and the second group of electrodes constituting, respectively, the first and the second generator of the standing acoustic longitudinal waves, are combined with reach other thereby forming a composite generator, which produces, simultaneously, one standing acoustic longitudinal wave that vibrates in the direction of the resonant length of the piezoelectric oscillator and one standing acoustic longitudinal wave that vibrates in the direction of the resonant height of the piezoelectric oscillator.
An electrode construction of this kind allows for the simultaneous excitation in the oscillator of, in particular, a standing acoustic longitudinal wave that vibrates along the resonant length of a piezoelectric oscillator and of a standing acoustic longitudinal wave that vibrates along the resonant height of the piezoelectric oscillator.
One advantageous motor construction is comprised of two or more plate-shaped piezoelectric oscillators that are connected to each other, thereby producing a uniform electro-mechanical resonator. In an embodied example of this kind of a piezoelectric motor, the excitation voltage of the piezoelectric oscillator is considerably reduced.
In one realization variant, the acoustically coupled oscillators that constitute the piezoelectric motor are connected to each other using a rigid organic bonding agent. This connection is particularly advantageous, in particular with regard to its simplified manufacturing technology. In the alternative, it is possible to combine the acoustically connected oscillators of the piezoelectric motor by way of sintering. This type of connection considerably improves the stability.
If a standing acoustic longitudinal wave with a constant preceding sign is excited in the piezoelectric motor in the direction of the resonant height of the piezoelectric oscillator, it is possible to arrange friction elements on one or on two side surfaces of the piezoelectric oscillator, in particular, in the areas with maximum vibration, which have the same preceding signs, of the standing acoustic longitudinal wave that vibrates in the direction of the resonant length of the piezoelectric resonator.
Arranging friction elements in this manner makes it possible to realize a movement of the friction elements of the piezoelectric motor that is aligned in the same direction.
In a piezoelectric motor in which a standing acoustic longitudinal wave with a variable preceding sign is generated that vibrates in the direction of the resonant height of the piezoelectric oscillator, the friction elements can be arranged on one or on two side surfaces of the piezoelectric oscillator, in particular, in the areas with maximum vibration, which do not have the same signs, of the standing acoustic longitudinal wave that vibrates in the direction of the resonant length.
Depending on the embodied example, the fiction elements for the variants of the piezoelectric motor according to the invention can be manufactured in the form of strips, small rods, pyramid-shaped elements or conical, cylindrical, or semi-spherical elements made of oxide-ceramic, metal-ceramic or of a corresponding composites with other materials.
Realizing the friction elements in this way allows for optimal adjusting to the driven element. Friction elements in the form of strips or small rods can have transverse grooves that make it possible to reduce the mechanical stresses developing between the friction element and the oscillator and that, moreover, prevent any deformation of the functional surface of the friction element. Depending on the respective embodied examples of the proposed motor, the friction elements can have a one-layered or multiple-layered structure.
This allows for an optimal adjustment of the friction elements to the respective piezoelectric oscillator. Depending on a respective concrete motor variant, layers of the one-layered or multiple-layered structure of the friction elements can be arranged parallel in relation to the side surfaces of the piezoelectric oscillator.
Arranging the layers of the friction elements in this manner allows for providing the friction elements with the maximum possible surface of friction contact that is able to transfer considerably greater forces than the embodied examples of a piezoelectric oscillator, motor or adjusting element that are known in the state of the art.
In another embodied example of the piezoelectric motor according to the invention, the one-layered or multiple-layered layer structure of the friction element can be arranged, in its entirety or in part, in a perpendicular direction in relation to the side surfaces of the piezoelectric oscillator. Arranging the layers of the friction elements in this way allows for the maximum possible suppression of parasitic, and therefore undesired, vibrations that are generated in the friction elements during the operation of the motor.
Another variant of an embodied example of the piezoelectric motor provides that the layers of the one-layered or multiple-layered structure of cylindrically, conically or semi-spherically realized friction elements are realized accordingly and that they are arranged concentrically. A layer arrangement of this type allows for a realization of the friction elements that places minimal stress upon the piezoelectric oscillator.
In the context of the embodied examples of the piezoelectric motor, the layers within the one-layered or multiple-layered structure of the friction elements have different moduli of elasticity. Varying the layers of the friction elements allows for optimally adjusting the friction elements of the piezoelectric motor to the piezoelectric oscillator.
As one realization, the wear resistant layer of the multiple-layered friction element of the piezoelectric motor has a modulus of elasticity that is determined on the basis of its capacity of resistance to wear and the mechanical stability of its functional surface, while a connecting layer of the friction element is characterized by a modulus of elasticity that is adjusted to the modulus of elasticity of the piezoelectric ceramic of the oscillator. This makes it possible to achieve an optimal acoustic adjustment of the friction element in relation to the piezoelectric oscillator.
In embodied examples of the piezoelectric motor with concentrically arranged layers of the friction elements, the wear resistant layer of the multiple-layered structure of the friction elements, suitably, has a modulus of elasticity that is determined on the basis of the required capacity of resistance to wear and the mechanical stability of its functional surface, while the properties of the dampening layer are determined on the basis of the dynamic stability of the wear resistant layer. As a result, a maximum possible dynamic stability of the friction elements is achieved.
In embodied examples of the piezoelectric motor with a two-layered or multiple-layered structure of the friction elements, it is possible to manufacture the layers of monolithic materials and to connect them to one another by way of sintering. This way, the maximum possible stability of the connection of the layers of the friction elements is reached.
In embodied examples of piezoelectric motors with a two-layered or multiple-layered structure of the friction elements, it is possible to envision a porous material as the connecting layers of the friction elements, which results in an improvement of the stability of the connection of the friction element with the surface of the piezoelectric oscillator.
The porosity of the materials within the layered structure of the friction elements can be realized as variable in this embodied example. In their entirety or in part, all layers can be comprised of a porous material that has variable porosity. Particularly suitable are realizations of piezoelectric motors with a multiple-layered structure of the friction elements in which the connecting layer has a maximum porosity and the wear resistant layer is not porous. An embodied example of this kind makes it possible to avoid jumps that are caused due to mechanical stresses within the friction element.
In another embodied example of the piezoelectric motor according to the invention, in particular embodied examples in which the layers of the friction elements are arranged in a perpendicular or concentric manner in relation to the side surfaces of the oscillator, the dampening layer is comprised of a porous material. This allows for maximum dampening of the friction element.
In the different variants of embodied examples of the proposed motor with a plane functional surface of the friction elements, this functional surface can be arranged at an angle in relation to the side surface on which the friction elements are arranged, resulting in an increase of the coupling force between the friction elements and friction layer.
In combination, the functional surface of the friction elements can have a triangular-concave or triangular-convex form or a round concave or round-convex form, and the functional surfaces of the friction elements are arranged along the resonant length of the piezoelectric oscillator. These variants of realizations of functional surfaces of friction elements enlarge the available surface of the friction contact.
In one embodied example, the friction elements of the piezoelectric motor according to the invention can be connected using an organic material, e.g. an epoxy-resin-based bonding agent, which is connected to the surface of the piezoelectric oscillator, resulting is a simplification of the manufacturing technology of the piezoelectric motor.
In the alternative, in another embodied example of the piezoelectric motor, it is possible to connect the friction elements to the surface of the piezoelectric oscillator using a material that creates a material-lock bond with the material of the oscillator. Suitable connecting materials are, for example, lead-containing easily fusible glass or other similar materials. This variant, which provides for establishing a connection between the surface of the piezoelectric ceramic and the friction elements, allows for maximum connecting solidity.
In the described variant of the piezoelectric motor according to the invention, it is possible to fill all or only some pores of the friction elements with a material that connects the friction element to the surface of the piezoelectric oscillator, thereby also creating a greater solidity of the connection.
In realizations of the piezoelectric motor according to the invention that feature transverse grooves, it is possible to fill the transverse grooves with a sound absorbing material, thereby reducing the mechanical quality of the friction elements. This dampens parasitic vibrations that develop in parts of the friction elements.
Moreover, the friction elements themselves can also be realized as glass strips that are melted onto the surface of the piezoelectric oscillator. This simplifies the manufacturing technology of the friction elements.
If the friction elements are manufactured as glass strips, they can be filled with a powder of a wear resistant material. Suitable for use in this context are, for example, powdered aluminum oxide, zirconium oxide, tungsten carbide, titanium carbide or another similar material. This improves the capacity of resistance to wear of the friction elements.
Envisioned as a suitable realization of the piezoelectric motor according to the invention is a realization that includes elements that limit the piezoelectric oscillator, thereby preventing any shifting of the piezoelectric oscillator in the direction of the resonant length. In an advantageous variant of a realization of a piezoelectric motor, the elements, which prevent the shifting of the oscillator, can serve as mechanical resonators whose frequency of resonance corresponds to the oscillation frequency of the piezoelectric oscillator during the operation of the motor. This reduces the mechanical losses.
In one embodied example of the piezoelectric motor according to the invention, the piezoelectric oscillator is equipped with at least one fastening element that is rigidly connected to the oscillator. Thus, the fastening elements allow for the possibility that the piezoelectric oscillator is rigidly fastened.
In a first embodied example, the fastening elements are arranged on at least one of the side surfaces of the piezoelectric oscillator, preferably in the locations of the minimum vibration of the standing acoustic longitudinal wave that vibrates along the resonant length of the oscillator. Arranging the fastening elements in this way makes it possible to affect a front fastening of the piezoelectric oscillator.
In another embodied example of the piezoelectric motor according to the invention, the fastening elements are arranged on at least one of the main surfaces of the piezoelectric oscillator, preferably at the locations of the minimum vibration of the standing acoustic longitudinal wave that vibrates in the direction of the resonant length of the oscillator. Arranging the fastening elements in this way makes it possible to affect a lateral fastening of the piezoelectric oscillator.
In another variant of an embodied example of the piezoelectric motor according to the invention, the fastening elements have the shape of a rectangular prism, a triangular prism, a semi-cylindrical prism or of another similar prism-type form; all the while, it is also possible to realize the fastening elements as conical elements, pyramid-shaped elements, semi-spherical elements or as rectangular elements with profile grooves or projecting parts, as cylindrical step elements or as round elements with profile bore holes. The corresponding realization of the construction of the fastening elements makes it possible to achieve a reliable attachment of the piezoelectric oscillators.
In further embodied examples of the piezoelectric motor according to the invention, the fastening elements are realized using a material whose modulus of elasticity is equal to or somewhat larger than the modulus of elasticity of the piezoelectric ceramic, in particular using oxide-ceramic. Realizing the construction in this manner ensures a high level of solidity of the fastening elements.
In one embodied example the fastening elements are comprised of a material whose modulus of elasticity is small in contrast to the modulus of elasticity of the piezo-ceramic of the piezoelectric oscillator. Realizing the construction of the fastening elements in this way makes it possible to achieve a reduction of the mechanical stresses that develop between the fastening element and the oscillator.
It is also possible to manufacture the fastening elements of the same type of piezo-ceramic as the oscillator. This way, an optimal acoustic coupling of the fastening element with the oscillator is achieved. Moreover, each fastening element, or a part thereof, can be manufactured of a porous material. This reduces the acoustic vibrations that develop inside the fastening element.
In special motors, it is also possible to realize the fastening elements as resonance bending plates or as resonance bending bars. Constructing the fastening elements in this manner allows for reducing the mechanical losses.
As components of the piezoelectric motor, the fastening elements can be connected to the surface of the piezoelectric oscillator, using an organic bonding agent. This simplifies the manufacturing technology of the motor.
Depending on the embodied example of the piezoelectric motor according to the invention, the fastening elements can be arranged on at least one of the side surfaces of the piezoelectric oscillator, in particular at the locations of the minimum vibration of the standing acoustic longitudinal wave that vibrates in the direction of the resonant length of the oscillator. This way, arranging the fastening elements in the form of a front fastening arrangement is made possible.
In another embodied example of the piezoelectric motor according to the invention, fastening elements are arranged on at least one of the main surfaces of the piezoelectric oscillator, in particular at the locations of the minimum vibration of the standing acoustic longitudinal wave that vibrates in the direction of the resonant length of the oscillator. This way, arranging the fastening elements in the form of a lateral fastening arrangement is made possible.
In one variant of an embodied example of the piezoelectric motor according to the invention, it is possible to set up the fastening elements inside solid support mountings. This allows for an especially stable fixation in place of the piezoelectric oscillator. In particular, the solid support mountings can be manufactured in the form of flat springs. This way, the mechanical losses caused due to the support mountings are reduced.
The driven element of the piezoelectric motor is, in general, arranged with the ability to shift. This makes longitudinal movements of the driven element possible. The driven element, which is arranged with the ability to shift, is realized, depending on its concrete modeling, as a rectangular platform, a frame or as a bar with rectangular, multiple-corner or round cross-section or as a tube. The results are varied options for modeling a piezoelectric linear motor.
In addition, it is possible to arrange the driven element with the ability to rotate. A motor construction of this kind allows for a rotational movement of the driven element. In the motor variants with the driven element arranged with the ability to rotate, the driven element can have the form of a cylinder, a plate, a hollow cylinder or of a ring.
The construction forms of the driven element that were referred to previously allow for the assembly of different variants of a piezoelectric revolving cylinder motor. In the context of the piezoelectric motor according to the invention, rectangular, round, elliptical or similar dampening bore holes are envisioned for the realization of the friction elements, preventing any expansion of acoustic waves, whose frequency is equal to the frequency of the piezoelectric oscillator during the operation of the motor or whose frequency is equal to harmonic oscillations, in the friction element. This makes it possible to improve the friction contact of the motor.
In accordance with the invention, the fiction layer of the driven element can be manufactured of oxide-ceramic or of a comparable other hard and wear resistant material, and, suitably, the thickness is at least five times smaller than the resonant height of the piezoelectric oscillator in order to effect as lasting a reduction as possible of the amplitude of the acoustic longitudinal vibrations that develop in the fiction layer.
The thickness of the fiction element located below the friction layer must be of a greater value than the resonant height of the piezoelectric oscillator in order for it to reduce the amplitude of the acoustic bending vibrations occurring in the driven element.
In accordance with the invention, it is possible to insert a thin dampening layer between the body of the driven element and the friction layer, that is comprised of a viscous organic or of a porous inorganic material or of a composite of the two in order to reduce the acoustic coupling between the friction layer and the driven elements.
The piezoelectric motor according to the invention can be comprised of at least two piezoelectric oscillators, arranged opposite to each other, and of at least two friction layers, arranged on two opposite sides of the driven element, in order to be able to forego a bearing for stabilizing the longitudinal movement.
To hold the driven element in an especially stable position, the piezoelectric motor according to the invention, in a special embodied example, is comprised of at least three piezoelectric oscillators and of at least three friction layers, which are arranged parallel in relation to each other and located in at least three planes.
In the embodied example of a piezoelectric motor according to the invention that has separate generators for longitudinal waves, the electric excitation source is realized as a two-channel power amplifier. Said amplifier is comprised of a first channel and of a second channel, of formation levels connected to a basic generator and of output power amplifiers that are electrically connected, via adjustment levels, to the corresponding electrodes of the generator on the piezoelectric oscillator. They generate acoustic longitudinal waves that vibrate in the direction of the resonant length of the piezoelectric oscillator as well as acoustic longitudinal waves that vibrate in the direction of the resonant height of the oscillator.
The setup of the electric excitation source with separate generators makes it possible to achieve optimal movement paths of the fiction elements in the oscillator, via the excited acoustic waves.
In another embodied example, the electric excitation source is set up as a single-channel power amplifier, which is comprised of a formation level, that is connected to the basic generator, and an output amplifier, which is connected, via an adjustment level and an electrode commutator, to the electrodes of the correspondingly composed piezo-generator.
The output power amplifiers are set up as bridge power amplifiers, each of which includes two half-bridges. The formation levels contain two excitation channels of the referred to half-bridge power amplifiers, and one of the excitation channels is equipped with a phase control element and contains a phase control input. This allows for regulating the rate of motion of the driven element.
As realization of the motor according to the invention, it is envisioned that the motor according to the invention is equipped with a signal level transformer whose output is connected to the phase control input of a phase control element. This allows for controlling the rate of motion of the driven element by way of a linear electric signal.
In another embodied example, the motor according to the invention is equipped with a demodulator of a pulse width modulated signal whose output is connected to the phase control input of the phase control element. This allows for controlling the rate of motion of the driven element by way of a pulse width modulated signal.
Furthermore, realizing the motor according to the invention including a level detector for the zero position, whose measuring input is connected to the input of the signal level transformer or to the output of the demodulator of a pulse width modulated signal, is also possible. In the above context, the output of the level detector is connected to the input of a reverse change-over or to the control input of an electrode commutator. This realization of the motor allows for reversing the driven element.
In another realization, the basic generator is equipped with a frequency control input. This variant of the motor allows for a frequency adjustment of the basic generator.
Also envisioned is a realization of the motor according to the invention with a phase detector; the phase detector is comprised of a first phase input and of a second phase input as well as of an output, and the output of the phase detector is connected to the frequency control input of the basic generator, the first phase input is electrically connected to the electrode of the same phase of the corresponding generator of acoustic longitudinal waves, and the second phase input is electrically connected to one of these waves. This allows for an automatic frequency adjustment of the basic generator.
In the embodied example of the motor according to the invention, separate generators of acoustic waves, a sensor is realized as a thin piezo-ceramic plates, containing electrodes on its large surfaces, and which is fastened, acoustically coupled, to the surface of the piezoelectric oscillator, in particular at locations of the greatest mechanical stress of the acoustic longitudinal wave that vibrates in the piezoelectric oscillator. This way, using the sensor, it is possible to determine the mechanical resonance of the oscillator that is excited by separate generators.
In the embodied example of the motor with composite generators of acoustic waves, the sensor is realized primarily in the form of two thin piezo-ceramic plates, containing electrodes on their wide surfaces, that are fastened, acoustically coupled, to the surface of the piezoelectric oscillator. Most suitably, they are fastened at locations in which the greatest mechanical stresses of the acoustic longitudinal wave occur as well as at those points that have, in the event of a signal phase shift of one of the channels of the power amplifier with regard to the signal of another channel by 180xc2x0 in relation to it, the same paths of movement. In this context, both sensor parts are connected to the second input of the phase detector by way of a sensor signal commutator. The phase detector control input is electrically connected to the control input of the reverse change-over. For this variant, the sensor also allows for a determination of the strength of the mechanical resonance of the piezoelectric oscillator.
The proposed motor can be equipped with a coordinate parameter sensor or movement parameter sensor of the driven element, which is electrically connected to the processor-controlled controlling means of the parameters measured by the sensor and whose output is connected to the signal level transformer or the demodulator of a pulse width modulated signal. This allows for adjusting the coordinate parameter sensor or movement parameter sensor of the driven element.